The materials which compose the Talbot formation consist of clays, loam, sands, gravel, peat, and ice-borne boulders.

The Recent

The Recent deposits embrace chiefly those being laid down to-day over the submarine portion of the Coastal Plain and along the various estuaries and streams. To these must also be added such terrestrial deposits as talus, wind-blown sand, and humus. In short, all deposits which are being formed under water or on the land by natural agencies belong to this division of geological time.

The Recent terrace now under construction along the present ocean shore-line and in the bays and estuaries is the most significant of these deposits and is the last of the series of terrace formations which began with the Brandywine, the remnants of which to-day occupy the highest levels of the Coastal Plain and which has been followed in turn by the Sunderland, Wicomico, and Talbot.

Beaches, bars, spits, and other formations are built up on this terrace belt and are constantly changing their form and position with the variations in currents and winds. Along the streams flood plains are formed that in the varying heights of the water suffer changes more or less marked. On the land the higher slopes are often covered with debris produced by the action of frost and the heavy downpours of rain which form at times accumulations of large proportions known as talus and alluvial fans. An illustration of the former is seen in the Devil's Race-course on the western slope of the Blue Ridge, the heavy blocks in this instance being separated by the action of frost and subsequently precipitated down the steep mountain side.

A deposit of almost universal distribution in this climate is the humus or vegetable mold which being mixed with the loosened surface of the underlying rocks forms our agricultural soils. The intimate relationship therefore of the soils and underlying geological formations is evident.

The deposit of wind-blown sands more or less important everywhere, as may be readily demonstrated at every period of high winds, is especially marked along the sea-coast in Worcester County where sand dunes of

considerable dimensions have been formed. Other accumlulations in water and on land are going on about us all the time and with those already described represent the formations of Recent time.

PRECIPITATION

SOURCE AND AMOUNT

The normal precipitation in this region, whether falling as rain, hail, sleet, or snow, ranges from 30 to 55 inches. This is greatest in the extreme western part of Maryland on the Alleghany Plateau, where the conditions favor both frequency and intensity of rainfall and snowfall. Throughout the Great Valley, that is, in eastern Allegany and Washington counties, the annual precipitation decreases rapidly; a second area of diminished precipitation is found over upper St. Mary's and the southern part of Charles County; and a third occurs over a narrow portion of the Eastern Shore bordering on the Atlantic, in Maryland and southern Delaware. In these three areas the normal annual precipitation is from 31 to 35 inches.

East of the Blue Ridge the annual precipitation increases, and throughout the Piedmont Plateau area it amounts to from 40 to 45 inches, being in general near the lower figure west of Parrs Ridge and near the higher figure east of Parrs Ridge.

A narrow area over which the normal annual fall is less than 40 inches lies just west of the Atlantic coast area already mentioned as one of the dry divisions, and a second limited area of this kind is found to embrace southwestern Kent County in Delaware and portions of Caroline, Talbot, Prince George's, Howard, and Baltimore counties in Maryland. With these exceptions, and that already noticed in portions of Charles and northern St. Mary's counties, Maryland, the normal annual precipitation for the Coastal Plain is from 42 to 48 inches. The bands of greatest precipitation in this latter area include southern Anne Arundel County, and from southern St. Mary's County northeastward over portions of Dorchester and Wicomico counties and southern Delaware.

The normal annual precipitation is divided throughout the seasons as follows: Spring and summer will have 11.5 to 12 inches, and fall and winter 9.5 to 10 inches.

Snowfall never fails completely even in the warmest winters, although it may be reduced to insignificant proportions except in the mountains.

DISPOSITION

Of the precipitation which falls as rain each year, a considerable portion immediately flows away in the surface streams and ultimately reaches the sea. The percentage of the rainfall which sinks into the ground to return to the surface to form springs after a longer or shorter journey, or which

is added to the underground water supply depends on several factors: (1) The character of the rains, whether slow and steady or torrential; (2) on the nature of the country, whether mountainous or flat or of intermediate type; (3) the character of the vegetation, whether thick and facilitating storage, or whether thin and thus with little influence in preventing rapid runoff; (4) on the character of the soil, whether porous and absorbent or heavy and close-grained, as rock or clays, and consequently more or less impervious; (5) and on the previous state of saturation of the underlying beds.

The amount of precipitation which falls in other forms than rain may act in a similar way in areas like Southern Maryland or the lower Eastern

Shore where snow seldom accumulates for long periods during the winter, while in the colder and particularly the mountainous regions snow may accumulate until the spring thaws, at which time it is subject to the influences just enumerated for normal rainfall.

The amount of precipitation that is lost by evaporation or that takes a part in chemical reactions in the ground is relatively negligible, and the amount that is extracted by the vital activity of the vegetation, while larger, is still a relatively small percentage.

SURFACE WATERS

The surface waters of a region may be grouped under the headings of streams, lakes, ponds, and swamps. Since lakes and ponds are prac

FIG. 75.-MAP SHOWING THE DRAINAGE BASINS.

tically absent throughout Maryland and Delaware, and since swamps are not sources of potable waters and are valuable hydrographically only as they act as storage reservoirs and thus prevent rapid and destructive runoff, the only surface waters to be considered in the present report are those of streams.

The greater part of the Maryland-Delaware region lies in the Atlantic drainage, but a small area in the western part of Maryland is drained by

the Youghiogheny River, whose waters ultimately find their way into the Gulf of Mexico by way of the Ohio River. The most important drainage areas are as follows: (1) The Youghiogheny River drainage, which includes the greater part of Garrett County; (2) the Potomac River drainage, which includes Allegany, Washington, and Frederick counties, and portions of Garrett, Carroll, Montgomery, Prince George's, Charles, and St. Mary's counties; (3) the western Chesapeake Bay drainage, which includes Harford, Baltimore, Anne Arundel, Calvert, and Howard counties, and portions of Cecil, Carroll, Montgomery, Prince George's, Charles, and St. Mary's counties; (4) eastern Chesapeake Bay drainage, which includes Kent, Queen Anne's, Talbot, Caroline, Dorchester, Wicomico, and Somerset counties, and portions of Cecil and Worcester counties in Maryland and the western parts of Newcastle, Kent, and Sussex counties in Delaware; (5) the direct Atlantic Ocean drainage, which includes a small area in Worcester County, Maryland, and the eastern part of Sussex County in Delaware, in which the streams flow directly into the Atlantic Ocean or its tributaries; (6) the Delaware River drainage, which in this area includes the restricted basins of numerous small creeks in Newcastle and Kent counties, Delaware, which are shown on the accompanying map as a part of the Atlantic drainage area. Most of the streams belong to one of two types, although there are some streams which exhibit the characteristics of both types in different portions of their courses. One type is found west of a northeast-southwest line, known as the "fall line," extending across the state through Wilmington, Elkton, Baltimore, and Washington. Here the streams have fairly steep gradients and flow over rocky beds. Their courses lie through a rolling country in which hard rocks prevail. Rapids and gorges are of frequent occurrence, and there are many opportunities for water-power development. Some of these have been utilized, but there are still many available power sites that are capable of yielding a large amount of horsepower.

East of the "fall line" the streams and the topography and geology have a different character. Here the country is less rolling and the surface formations are unconsolidated sands and clays. The streams flow